The transmission reliability of any communication system is surely reduced due to the influence of the transmission medium. In order to improve the transmission reliability, modulation-demodulation and channel coding-decoding are usually required to be designed for the receiving and transiting ends, especially in the wireless transmission system.
Each modulation and coding scheme (MCS) combination has a corresponding spectral efficiency, e.g., the combination of a QPSK modulation and a convolution code or Turbo code with a code rate of ½ can achieve a transmission efficiency of 1 bit/symbol. Multiple MCS combinations can be achieved by changing the modulation order (QPSK, M-PSK, 16QAM, M-QAM, etc.) and the code rate (½, ⅔, ¾, etc.). Different MCSs can be applied to different transmission environments. E.g., a channel of a good transmission environment can transmit more information with the MCS of a higher spectral efficiency; whereas a channel of a poor transmission environment can transmit less information with the MCS of a lower spectral efficiency, so as to ensure the transmission quality.
Generally, in a communication system, the transmission conditions can be indicated by the received signal to interference plus noise ratio (SINR). Of course, the channel quality can also be indicated with other indexes. Under a given SINR, in order to meet certain transmission requirement, such as that the transmission error rate is below certain threshold (e.g., 10% block error rate (BLER)), the MCS of a spectral efficiency as high as possible may be selected. Each MCS has a different BLER under a different SINR, and this can be indicated with a BLER-SINR graph. The transmission throughput of the system can be improved as far as possible by selecting different MCSs in accordance with different received SINRs, and this technique is called as adaptive MCS selection. The variation range of the received SINR depends on many factors, such as system configuration, transmission medium distribution, user state change in system service, etc. Taking the cellular mobile wireless communication system as an example, a user close to a base station experiences less wireless signal transmission attenuation, and the received SINR is higher, while a user far from the base station experiences more signal attenuation, and the received SINR is lower; with respect to a cellular system having a reuse factor of 1 in multiple base stations, a user at the edge of the cell is interfered by a non-service base station, thus the SINR is lower than that of a user at the cell center. In a word, the magnitude of the received SINR to each user depends on factors such as system configuration, user state, etc. Statistically, the magnitude of the received SINR to a user can be indicated by probability distributions, such as cumulate density function (CDF) or probability density function (PDF). From those distribution curves, the variation range of the user SINR in the system can be approximately known.
In order to utilize the system capacity as far as possible, an adaptive MCS selection shall reflect the condition of the current transmission channel, i.e., to select a MCS of a spectral efficiency as high as possible, which meets the BLER requirement, under the current received SINR value. Of course, the receiving end shall, in certain way, inform the transmitting end of the selected MCS, so that the transmitting end can transmit correctly. As transmitting MCS message also occupies the transmission channel, the number of MCS combinations supported by the system shall be limited, and many communication standards specify MCS combinations supported both by the transmitting and receiving parties. For instance, IEEE 802.16E [1] specifies the following 11 MCS combinations: QPSK ½ with a repetition factor of 6, QPSK ½ with a repetition factor of 4, QPSK ½ with a repetition factor of 2, QPSK ½, QPSK ¾, 16 QAM ½, 16 QAM ¾, 64 QAM ½, 64 QAM ⅔, 64 QAM ¾, and 64 QAM ⅚.
The current research mainly discusses designing the MCS structure under a given spectral efficiency, namely designing the modulation scheme and the coder structure, so that the BLER-SINR curve is more steep, i.e., the BLER is smaller under the given SINR. However, in an aspect of system design, when a number of MCS combinations is given, how to design the MCS and spectral efficiency level (i.e., which MCS and spectral efficiency level are to be supported by the system), so that the system capacity is maximized, is very important for improving the whole performance of the communication system.
The references of the present application are listed as follows, and incorporated herein by reference, as described detailedly in the Description.
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